1. Field of the Invention
The present invention relates to a multichannel radar system for use on motor vehicles such as automobiles.
2. Description of the Prior Art:
Radar systems mounted on motor vehicles such as automobiles are used in combination with alarm and/or indicator devices for helping to prevent collisions between motor vehicles and also between motor vehicles and other objects. Such radar systems on motor vehicles are required to detect small ranges of about several tens centimeters because they should be used to give warnings against collisions between motor vehicles in small ranges such as upon traffic jams and also against collisions between motor vehicles and objects such as when they are parked in garages. In view of such a requirement, AM and FM radar systems are preferable to pulse radar systems for use on motor vehicles. The carrier in such AM and FM radar systems should preferably be in a millimeter wave range, particularly in the vicinity of 60 GHz which is noted for its high absorption by oxygen, in order to achieve smaller radar module sizes and avoid interference with existing microwave communications systems.
FM radar systems which employ millimeter waves are disclosed in U.S. Pat. Nos. 5,181,037, 5,229,774, and 5,369,409, for example.
Radar systems installed on motor vehicles should radiate a number of beam signals for detecting obstacles or targets which may possibly be located in a relatively wide space in front and laterally of the motor vehicle. To meet such a requirement, the radar systems on motor vehicles have a number of transmission and reception channels for transmitting beam signals and receiving reflected signals. The radar systems on motor vehicles also have large power requirements because they employ low-efficiency ultra-high -frequency electronic devices including oscillators and modulators that operate in a millimeter wave range. The conventional radar systems disclosed in the above U.S. patents have a single signal generator that operates all the time which produces an output signal to be distributed among transmission channels through an intermittently operated switching device or amplifier. Such a single signal generator consumes a relatively large amount of electric power. It is important that the radar systems on motor vehicles have reduced power requirements as all the DC electric power needed to operate the radar systems has to be generated on the motor vehicles Lower power consumption by radar systems is more important on electric vehicles which will be expected to find more use in the future.
In the event of a failure of the radar system on a motor vehicle, if the driver of the motor vehicle is unaware of the malfunction of the radar system, then the motor vehicle will be in a dangerous situation because the driver drives the motor vehicle relying upon the detecting and alarming capabilities of the radar system. Inasmuch as the conventional radar systems have a single signal generator, if the single signal generator becomes defective, then all the transmission channels fail to operate.
The radar systems installed on motor vehicles normally operate on the time-sharing principles in that beam signals are time-division-multiplexed for radiation from a plurality of respective antennas. For reducing the power requirements of the time-sharing radar systems, DC voltages supplied to signal generators and amplifiers thereof are periodically turned on and off. However, when the DC voltages supplied to the signal generators and amplifiers are periodically turned on and off frequently, their electric characteristics tend to be unstable, lowering the detecting accuracy of the radar systems.